Despite significant advances in neonatal intensive care, including directed antibiotic therapy, mortality from neonatal sepsis remains significant with more than three million deaths worldwide. The highest risk of mortality occurs in preterm, low birth weight (LBW) and very low birth weight (VLBW) neonates. During the initial funding period of this award, we made three novel observations: 1) the neonate relies predominantly on its innate immune system to recognize infections and to provide early protective immunity, 2) host innate immunity is also defective due in part to a failure of innate immune cells to recognize and respond to chemokines essential for recruitment and activation, and 3) adjuvant treatment of mice with TLR and NLR agonists can stimulate PMN function, improve protective immunity, and increase survival to sepsis through MyD88- and inflammasome-independent pathways. Based on these findings, our ultimate goal is to develop adjuvant- therapies based on TLR signaling that can reduce the incidence and severity of both early and late sepsis in LBW/VLBW infants. To accomplish this, there are three specific aims: 1) To delineate the mechanism by which pretreatment of neonates with TRIF-specific pattern recognition receptor (PRRs) agonists improves survival in neonatal sepsis; 2) To determine the mechanisms by which immune adjuvants improve protective immunity and outcomes to neonatal sepsis; and, 3) To determine whether LBW and VLBW infants express comparable defects in PMN chemotaxis, ROS production and bacterial killing seen in PMNs from murine models of neonatal sepsis, and whether treatment of these human cells with TLR4 agonists restores innate immune function. The first two specific aims will determine the mechanisms by which pretreatment of neonatal mice with TRIF-specific TLR4 agonists with and without alum adjuvants improves outcome from E.coli and polymicrobial sepsis. The final specific aim will validate whether the protective effect of TLR agonists and alum seen in neonatal mice are recapitulated in cord and peripheral blood from full-term and LBW/VLBW infants. The ultimate goal of these studies is the reduction of early and late sepsis with improved survival in the highly vulnerable LBW/VLBW infant population by augmenting their immature innate immune system. Ultimately, it is our goal (at the end of this proposed funding period) to move novel or FDA-approved adjuvants and unique TRIF agonists into preliminary clinical trials in LBW/VLBW infants at risk of developing sepsis.